In multiple-energy projection radiographic imaging, a number of images of the same object are acquired that reveal the x-ray transmittance of the object for differing x-ray spectra. In dual energy imaging, two images of the same object are acquired sequentially under different x-ray beam conditions, such as beam energy and filtration. These images are proportional to the x-ray transmittance of the object for the differing x-ray spectra. These images can then be decomposed to produce material specific images, such as soft-tissue and bone images. Radiographic imaging procedures that require multiple exposures, such as dual energy imaging, may acquire multiple images over a period of time.
Lung cancer presents an burden to society because survival is low for advanced stage disease. The key to survival is early detection. Conventional chest radiography has proven inadequate in the detection of early-stage disease, missing 50% of nodules measuring 10 mm or less. The lack of sensitivity is attributed in large part to the superposition of anatomical structures in the projection image, i.e., the obscuration of subtle soft-tissue nodules by overlying “anatomical noise,” such as the ribs and clavicles. Low-dose CT (LDCT) offers some improvement in diagnostic sensitivity; however, diagnostic specificity (as well as increased cost and radiation dose) presents a remaining challenge.
Dual-energy (DE) imaging has been investigated for detection of lung disease.
Conventionally, DE imaging has been limited by clinical implementation, a relatively high radiation dose, and the lack of a high-performance detector. The availability of digital detectors (also referred to as flat-panel detectors (FPDs)) offering real-time digital readout and performance consistent with the demands of chest radiography, however, promises to remove conventional limitations, permitting high-performance DE imaging at total dose equivalent to that of a single chest radiograph. Further, such renewed interest in DE imaging using FPDs extends beyond chest imaging to include real-time DE fluoroscopy (e.g., vascular and cardiac interventions) and DE computed tomography. In each case, it is desired to maximizing DE imaging performance.
The present invention describes the DE image acquisition techniques for a chest imaging system. Factors are described for dual-energy filtration, kVp-pair, and allocation of dose between low- and high-kVp projections. It is desired to maximize soft-tissue visibility of lung nodules in DE soft-tissue images.